This invention relates to improved hot melt adhesive compositions utilizing a hydrogenated substantially aliphatic tackifying resin having a high glass transition temperature. The adhesive compositions have surprisingly high heat resistance combined with good cold temperature flexibility, light color and excellent color stability.
Hot melt adhesives generally comprise a thermoplastic polymeric component, a tackifying resin component and either a wax component, plasticizing component or a combination thereof.
The tackifying resin is known to provide specific adhesion and to increase peel values which translates into heat resistance. The tackifying resin also generally has the biggest impact on the color of the adhesive. Aesthetic appeal has become extremely important to adhesive users.
Commonly used tackifying resins include those which are rosin derived including gum rosin, rosin acid and rosin ester resins, petroleum derived hydrocarbon resins and terpene based resins which can be derived from d-limonene. These resins may be modified further to add functionality or aromaticity through the addition of phenolic groups or styrene groups, for instance.
It is a constant struggle on the part of adhesives chemists to improve both the heat resistance and cold temperature resistance of hot melt adhesives. The resistance of hot melt adhesive compositions to fluctuations in temperature are particularly important for shipping goods across country through desert conditions as well as through the northern regions in the winter months, and also for storage in warehouses which often may be subject to ambient conditions.
Higher heat resistance is generally achieved through the use of higher levels of tackifying resin and/or higher levels of wax that will typically adversely affect the cold temperature resistance. Good cold temperature resistance is generally improved through the use of liquid components and/or higher levels of the polymer that will typically adversely affect the heat resistance. The polymeric component is often the component in the hot melt adhesive having the lowest glass transition temperature. Hence, it is difficult to improve both of these two critical features of an adhesive formulation simultaneously, since generally one is improved at the expense of the other.
High heat resistance has been achieved through the use of high melting point phenolic modified terpene resins. However, there are safety hazards associated with the production of such resins due to the toxicity of phenol. The cost of these modified terpenes is also higher than petroleum based resins due to the different feedstreams, and also due to the cost of adding the phenol, thereby raising the cost of adhesives to end users which in turn makes them less attractive for large scale production.
Petroleum based hydrocarbon resins are popularly used in the adhesives industry due to availability and economics. These resins may be derived from many different feedstreams produced during the petroleum cracking process including C5, C8, C9 and C10. Dicyclopentadiene based resins are derived from C10 feedstreams that contain various components of which DCPD may be the major component.
U.S. Pat. No. 4,102,834 to Morimoto et al. issued Jul. 25, 1978 teaches a hydrocarbon resin having a number average molecular weight of 300 to 2500, a softening point of 40xc2x0 C. to 180xc2x0 C., a bromine number of 5 to 100 g/100 g, and a Gardner color of 5 to 17. All resins exemplified have softening points from 98xc2x0 C. to 106xc2x0 C. The final resin is comprised of the polymerization product of a hydrocarbon fraction boiling within the range of 135xc2x0 C. to 280xc2x0 C., which contains various hydrocarbons, and dicyclopentadiene. The resultant resin contains, based on the total weight thereof, 20% to 80% of a unit derived from the dicyclopentadiene.
U.S. Pat. No. 4,629,766 to Malatesta et al. issued Dec. 16, 1986 teaches an improved method of hydrogenating hydrocarbons obtained from the polymerization of various petroleum based feedstreams. The resin feed exemplified therein was a solution of a thermally polymerized hydrocarbon resin obtained by polymerizing a feedstream containing 60 wt-% to 70 wt-% polymerizable monomers comprising substituted and unsubstituted C5 cyclic olefins and C10 bicyclic diolefins. No specific adhesive compositions are disclosed.
U.S. Pat. No. 5,410,004 issued Apr. 25, 1995 and U.S. Pat. No. 5,691,432 issued Nov. 25, 1997 both to Williams teaches tackifying resins polymerized from dicyclopentadiene monomer and their use in inks, adhesives, coatings and other related areas. These resins are made in the presence of a Bronsted acids, are unhydrogenated and have Gardner colors in the range of 3 to 5.
U.S. Pat. No. 5,552,489 to Merrill et al. issued Sep. 3, 1996 teaches a process for producing tackifiers through the use of a single-site catalyst with an alpha-olefin and a cyclic monomer under conditions designed to produce low molecular weight. Dicyclopentadiene is disclosed as a suitable cycloolefin comonomer but is taught only in combination with an xcex1-olefin comonomer as well.
U.S. Pat. No. 5,171,793 issued Dec. 15, 1992 to Johnson et al. teaches thermally polymerized hydrocarbon resin and a novel process for hydrogenating said resin wherein the resin is a copolymer of a feed which is a mixture of styrene and indene and derivatives thereof and cyclodiene monomers and dimers and optionally acyclic dienes.
It is an object of the present invention to teach the utilization of dicyclopentadiene based hydrocarbon tackifying resins to achieve improved hot melt adhesive compositions.
This invention relates to an improved hot melt adhesive composition comprising about 20% by weight to about 50% by weight of at least one substantially aliphatic tackifying resin having a glass transition temperature of 65xc2x0 C. or higher, about 20% by weight to about 50% by weight of at least one thermoplastic polymer. The resin is preferably a hydrocarbon tackifying resin, derived at least in part, from dicyclopentadiene. The thermoplastic polymer is preferably a homopolymer, copolymer or terpolymer of ethylene, an amorphous polyalphaolefin, a rubbery block copolymer, a homogeneous ethylene/xcex1-olefin interpolymer, and mixtures thereof; and 0% by weight to about 40% by weight of at least one wax. In embodiments that employ a homopolymer, copolymer or terpolymer of ethylene, the total tackifying resin concentration is equal to or less than the total polymer concentration. The glass transition temperature of the tackifying resin is preferably greater than about 70xc2x0 C.
In another embodiment, the present invention is an adhesive composition comprising from about 10 wt-% to about 80 wt-% of at least one hydrocarbon tackifying resin derived at least in part from dicyclopentadiene and having a Tg greater than about 65xc2x0 C. and from about 10 wt-% to about 80 wt-% of at least one amorphous polyalphaolefin and/or block copolymer. The tackifying resin is preferably derived predominantly from dicyclopentadiene.
The glass transition temperature of the tackifying resin is greater than about 65xc2x0 C., preferably greater than about 70xc2x0 C., more preferably greater than about 75xc2x0 C., and most preferably greater than about 80xc2x0 C. The melting point of the tackifying resin as measured by the ring and ball softening point is greater than about 135xc2x0 C. and preferably greater than about 140xc2x0 C.
The adhesive composition preferably has peel values of greater than about 60xc2x0 C., more preferably greater than about 65xc2x0 C., even more preferably greater than about 70xc2x0 C., and most preferably greater than about 75xc2x0 C. Further, the viscosity of the adhesive composition is typically less than about 10,000 cPs at about 175xc2x0 C., preferably less than about 5000 cPs, more preferably less than about 3500 cPs and most preferably less than about 2000 cPs at about 175xc2x0 C. Surprisingly and unexpectedly, in light of the high heat resistance, the resultant composition has good cold temperature flexibility.
These adhesives are primarily useful for non-pressure sensitive adhesive applications including bookbinding, packaging and structural applications including wood, construction, automotive, appliance, other types of durable goods and so forth.